Chronic kidney disease: 'Silent killer' may have multiple triggers

Why are thousands of sugarcane workers in Nicaragua are dying from chronic kidney disease each year? Sasha Chavkin, of The Center for Public Integrity, discusses what may be behind this mysterious epidemic.

By Stacey Naggiar, NBC News

Scientists hunting for a “silent killer” in the jungles of Nicaragua believe they have identified one reason that sugarcane workers are dying of kidney disease at an astounding rate, but they also are uncovering clues suggesting that other factors are contributing to the mysterious epidemic.

According to Dr. Andrew Narva, director of the National Kidney Disease Education Program, cases of chronic kidney disease, or CKD, are extremely unusual among men in their 20s and 30s who don’t suffer from an associated medical condition, typically high blood pressure or diabetes.

But those diseases are maladies of the developed world, not something that would trigger an epidemic striking down legions of adult men in the prime of their lives in rural Nicaragua and elsewhere.

Yet that’s just what’s happening. According to an analysis of World Health Organization data by the International Consortium of Investigative Journalists, kidney failure claimed the lives of 2,800 men a year from 2005 to 2009 in Central America. Most of those men were sugarcane workers doing manual labor in the hot and humid fields.

With diabetes and hypertension ruled out, what could be to blame?

Epidemiologists and other experts looking at the unexplained cluster of CKD in Nicaragua have several theories.

An inexplicable epidemic in Central America, where more than 16,000 people — mostly sugarcane workers — have died from incurable chronic kidney disease. NBC's Kerry Sanders reports from Nicaragua.

Dr. Daniel R. Brooks, associate professor of epidemiology at the Boston University School of Health, has long believed that severe dehydration due to extreme heat stress has been wreaking havoc with the agricultural workers’ kidneys.

But Brooks recently found early signs of kidney disease in adolescents in Nicaragua who had not been performing manual labor. This finding suggests that an environmental factor may be partly responsible for the epidemic.

Brooks told Center for Public Integrity reporter Sasha Chavkin, who has played a leading role in publicizing the medical mystery, that “while dehydration and strenuous labor may be an important cause, it’s unlikely to be able to explain the epidemic on its own.”

Dr. Richard Johnson, chief of the Division of Renal Diseases at the University of Colorado, who also is investigating the deaths, agrees that heat stress and severe dehydration likely play a role in triggering the disease. But he suspects that a form of rehydration peculiar to sugarcane workers also may contribute.

The workers frequently slice a stalk of cane, peel it and pop it in their mouths, where it produces a sweet sugary liquid. That, Johnson theorizes, may be causing a toxic effect to a particular region of the kidney. Moreover, the effects of sucrose on the kidneys may be amplified because the cane workers are already severely dehydrated, said Johnson, who is conducting laboratory studies to test the theory.

A new investigation by the WHO and Sri Lanka’s health ministry of a similar outbreak of CKD there has uncovered yet another possible culprit. Tests of rice-paddy workers found higher-than-expected levels of arsenic and cadmium in their systems, raising the possibility that the heavy metals, which are used in fertilizers, could be infiltrating the food chain. The agencies’ final report is expected to be released later this month.

What is CKD?The kidneys are responsible for a tremendous amount of metabolic activity. They filter 3 to 4 ounces of blood plasma per minute, removing excess waste and water that is excreted from the body in the form of urine.

Narva, the National Kidney Disease Education Program expert, said that chronic kidney disease is the result of repeated damage to the kidneys.

It is diagnosed on the basis of one of two criteria: a kidney that is filtering less than half the amount of blood than normal for three consecutive months or evidence of kidney damage independent of the filtration rate -- blood in the urine or a kidney biopsy that shows disease, for instance.

In the U.S., Narva estimates only 10 to 15 percent of CKD cases are primary, meaning they are not secondary to high blood pressure or diabetes.

Dr. Leslie Spry, who has been treating patients with kidney disease for over 30 years, said secondary CKD in which diabetes and hypertension are involved occurs as prolonged damage to the glomeruli, round structures in the bean-shaped kidney where the blood-filtering takes place. Symptoms in these patients often include fluid retention and swelling in the ankles.

But the form of the disease affecting the cane workers in Central America is “almost universally asymptomatic,” meaning the afflicted often have no adverse side-effects until the disease is in the advanced stages, Spry explained. That means the disease can damage the organ for months and potentially years without the patient knowing, which is why kidney disease is often referred to as “the silent killer.”

In these cases, tubules in the kidney become damaged, causing “interstitial nephritis” – or swelling in the space between the other structures in the organ, Spry said. Over time patients stop eating, lose weight and suffer complications such as pneumonia or other infections that can cause death. Also, potassium can eventually build up in the blood to such a high level that the heart stops, he said. That poison is responsible for the intense pain that accompanies the final stages of death by CKD.

In his own words, Maximiliano Lopez describes an average day in the life of a sugarcane cutter and how he's coping with the chronic kidney disease that he expects will soon kill him.

Depending on the severity of the kidney damage, “Death could occur in as little as one to two years, as we’ve seen in the past with lead exposures,” Spry said.

Patients with kidney disease are categorized by stages, which are based on a measure called glomerular filtration rate (GFR), he said. If a patient reaches stage four, dialysis -- a treatment in which blood is filtered outside of the body – is required. Without treatment CKD will progress to end stage renal disease, at which point the kidneys either shut down completely or barely continue to function. At that point, a kidney transplant is required to avert death.

In the case of the poor and uninsured sugarcane workers, treatment by dialysis and organ transplants are both too expensive and nearly impossible to obtain, making diagnosis of CKD tantamount to a death sentence.

Mike Gagné, a 32-year-old resident of Rochester, N.Y., can empathize with their plight, as he was fortunate to avoid their fate.

Gagné was one of the 20 million Americans 20 and older afflicted by CKD, according to the federal Centers for Disease Control.

He said he began experiencing high fevers and fatigue in 2007. He also began losing weight, was anemic and had a chronic metallic taste in his mouth.

He said he saw infectious disease specialists, rheumatologists and other physicians, but they were unable to provide a diagnosis, labeling his malady “a fever of unknown origin.”

Then, seven to eight months after he noticed the symptoms, Gagné was told his kidneys were failing. In 2009, he was told he needed a transplant to survive.

Gagné was fortunate in more ways than one. The disease was caught early enough that he was able to enter a donor screening program before dialysis was necessary. And in 2010, underwent a successful kidney transplant after an aunt volunteered to be a donor.

He said he can only imagine what it would be like to suffer from the disease without recourse to treatment, let alone a cure.

“I don’t think people really know what it is and the impact it has on the person that’s dealing with it in terms of how much it impacts the body and your overall day to day life,” he said.